Method for heating molten metals in a vacuum chamber



Oct. 27, 1964 A. LORENZ 3,154,404

METHOD FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Original Filed Nov.24, 1958 2 Sheets-Sheet 1 ELECTRICAL POWER SOURCE DIFFERENTIAL ANDACTUATOR A MOTORS MECHANICAL FIG. I

Oct. 27, 1964 A. LORENZ 3,154,404

METHOD FOR HEATING MOLTEN METALS IN A VACUUM CHAMBER Original Filed Nov.24, 1958 2 Sheets-Sheet 2 FIG. 2

United States Patent f 3,154,494- METHUD FOR HEATING MOLTEN METALS IN AVACUUM CHAMBER Albert Lorenz, Hanan am Main, Germany, assignor to W. (3.Heraeus G.m.b.H., Hanan am Main, Germany Original application Nov. 24,1958, er. No. 775,791, new Patent No. 3,61%,275, dated .Fan. 30, 1962.Divided and this application Jan. it), i961, Ser. No. 81338 Claimspriority, appiication Germany Nov. 26, 1957 ll Claim. (Cl. 75-16) Thepresent invention relates to a method and apparatus for heating metals,and especially steel, for the purpose of extracting the gases therefrom.This application is a division of application Serial No. 775,791, filedNovember 24, 1958, now United States Letters Patent No. 3,019,275.

Prior to this invention the gases occluded in molten metals, especiallysteel, were extracted therefrom by passthe metals in a continuous flowthrough an evacuated chamber. Numerous efforts were then made to improvesuch gas extraction by further heating the metals while the extractionprocess was being carried out. This was done by providing arc-heating orresistance heating means within the closed evacuated chamber or bymaking a part of such chamber in the form of a crucible and surroundingsuch part with an induction coil. However, these prior methods either donot operate safely and reliably or only very inefficiently since they donot heat up the entire mass of the metal flowing through the evacuatedchamber, but only a small part thereof, that is, either only the surfaceof the metal or only a negligible amount in comparison to the volume ofthe flow.

It is an object of the present invention to provide a new andsurprisingly simple method of heating up the flow of molten metal withinthe evacuated chamber for the purpose of increasing the efficiency ofthe gas extraction considerably over the methods hitherto employed.

A further object of the invention consists in the provision of a newapparatus for heating up the flow of molten metal while passing throughthe evacuated extraction chamber by inducing electric currents withinsuch flow of molten metal in a new and highly improved manner.

Instead of merely heating up a small portion of the flow of molten metalwithin the evacuated extraction chamber, the present invention providesfor a thorough heating of the entire volume of the flow of metal. Forthis purpose, the present invention utilizes a gas extracting apparatusof the type in which the molten metal is withdrawn from a containerholding the metal along one path, then passed through an evacuatedextraction chamber, and finally returned to the container along a Isecond path which is spaced from the first path. Ac-

cording to the invention, electric heating currents are then produced byinduction within the entire amount of molten metal of such circulation.This is attained by the provision of a transformer, the secondarycircuit of which is formed by the flow of molten metal and the closedcore of which passes between the two mentioned paths of the flow ofmetal and carries a primary induction coil which is energized by analternating current of a standard frequency. As soon as the molten metalflows over from the first or intake path into the second or return path,the secondary circuit of the transformer will be closed and it therebyreacts upon the current flowing through the primary coil. The beginningof this reaction may be utilized for indicating the beginning of thecontinuous gas-extraction process, and the strength of this reactionupon the primary current produced by a stronger or weaker flow of moltenmetal may also be 3,154,404 Patented Oct. 27, 1964 utilized foreffecting and controlling the gas-extraction process.

These and further objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription thereof, particularly when read with reference to theaccompanying drawings, in which FIGURE 1 shows diagrammatically andpartly in section one preferred embodiment of the present invention;while FIGURE 2 shows a cross section taken along line A-A of FIGURE 1.

Referring to the drawings, the container or ladle 1 holds the moltenmetal 2 from which the gases occluded therein are to be expelled bymeans of the gas-extraction apparatus 3 which is partly immersed fromabove into the metal bath. This apparatus consists of an extractionchamber 5 which is continuously evacuated through a pipe 4 leading to apump and control valve unit 4'. Chamber 5 has a pair of pipes 6 and '7extending vertically downward therefrom and into the bath of moltenmetal 2 at a considerable distance from each other. By injecting a gasthrough a pipe 3 into inlet pipe 6, a continuous flow of metal will bestarted and maintained, rising from the bath in ladle it through pipe 6into chamber 5, and then flowing through this chamber toward the returnpipe 7 and through the latter back into the bath in ladle 1. The gasbubbles then rising in pipe 6 will take along the metal and convey itupwardly into the actual extraction chamber 5. The gas supply may beregulated by a suitable valve mechanism 8'. A suitable hopper 9 or thelike containing alloying constituents is also connected to chamber 5 forsupplying these materials to the flow of metal passing through thechamber. Hopper 9 is likewise adapted to be sealed hermetically towardthe outside, and it is provided with suitable means, as diagrammaticallyindicated at 10 in FIGURE 1, for controlling the supply of thesealloying constituents into chamber 5.

The gas extracting apparatus as such is enclosed by a metallic covering11 which is adapted to take up the outside pressure acting upon theapparatus, and it is provided at the inside with a lining of refractorymaterial. Covering 11 also extends around the intake and return pipes 6and 7 to a point closely above the surface of the bath of molten metal 2in ladle ll. Thus, the pipe portions extend ing into the bath of metalonly consist of refractory material and are carried by the metalcovering 11.

interposed between the inlet and return pipes 6 and 7 is a practicaliyciosed iron transformer core 12 which also carries a primary coil 13which is supplied with an alternating current of a standard linefrequency. B means of this transformer core 12 a very strong alternatingcurrent will be induced in the molten metal fiowing from the bath 2 inladle 1 through inlet pipe 6, chamber 5, and return pipe 7 back intobath 2. The path of the current in the metal bath 2 is indicated inFIGURE 1 by the dotted line 14. Since the cross-sectional area of thebath itself is very large, the resistance incurred by the currentpassing therethrough is very small. As the metal covering 11 of theapparatus does not extend entirely to the surface of the metal bath 2,there is no danger of a short circuit of the induced current due to suchcovering. Within the extraction cham ber 5, however, the molten metalflows from inlet pipe 6 to return pipe 7, and during such passage itstrongly sprays and spatters. The cross-sectional area of the moltenmetal which is present at this passage at all times is thereforerelatively small, with the result that the electric resistance and theheating effect produced within the metal in the chamber itself is veryhigh.

The heat is therefore generated primarily within the upper part of theheated path 2-65-72 of the molten metal. This, however, is the placewhere only a small amount of the molten metal is separated from thegreat mass of the bath 2 and where it is therefore to be expected morethan at any other place that the molten metal will cool off or may evensolidify. On the other hand, this is also the point where relativelycold alloying constituents may be added from the hopper 9 by its feedcontrol device 10. It is therefore necessary that the heat required formelting or dissolving these additions will also be supplied at thispoint.

The most important requirement for carrying out the method according tothe invention is the fact that the molten metal passing through theapparatus always has to form a closed electric circuit. Obviously thecirculation of the molten metal by means of an added gas as previouslydescribed may also be attained by difierent means, for example, bycentrifugal conveying means of the type described in the inventorsprevious United States Letters Patent No. 2,893,860, or the like.

The method according to the present invention has, however, certainother very important advantages. As already stated, the uninterruptedcirculation of the molten metal forms the secondary circuit of atransformer. This secondary circuit is closed after the apparatus hasbeen evacuated and the conveying gas has been introduced through pipe 8and at the very moment when the molten metal flows over from pipe 6 topipe 7. After the electric current has been switched on to operate thetransformer 12, 13, this moment may be easily determined by an ammeter15. This serves as a clear indication of the fact that the continuousgas extraction process has been started. The ammeter will also indicateany interferences in the normal operation of the apparatus, for example,an interruption in the continuous flow of metal, and the like.

The strength of the alternating line current which may be about 100 kw.or more may, however, to a certain extent also furnish an indication ofthe volume of the flow of metal through vacuum chamber 5. The amperageindicated by ammeter may therefore indicate the volume and velocity ofthe flow and it may also be used for controlling the flow, for example,by an adjustment of the position and elevation of the gas extractingapparatus relative to the bath of molten metal 2 vertical positioningdevice indicated generally at 16, by an adjustment of the amount ofconveying gas supplied through pipe 8, or by an adjustment of the outputof the evacul ating pump and control unit 4' which is connected to pipe4, or by similar means. Such adjustments may also be producedautomatically by suitable means known in the art which operate inresponse to the indication of ammeter 15 and the changes in the strengthof the primary current.

Fromthe above description, it will be clearly apparent that the newmethod of expelling the gases occluded in a molten metal, andparticularly in steel, is very simple and highly efficient, and requiresonly a very simple and relatively inexpensive apparatus.

Although my invention has been illustrated and described with referenceto the preferred embodiments thereof, I wish to have it understood thatit is in no Way limited to the details of such embodiments, but iscapable of numerous modifications within the scope of the appendedclaim.

Having thus fully disclosed my invention, what I claim In the method oftreating molten metal by circulating the molten metal from a containerzone having a large cross-sectional area in an amount of lessercross-sectional area via a first path to a molten metal treating zone,said molten metal entering said treating zone and passing therethroughwhile strongly spraying and spattering, thence through said treatingzone and thereafter via a second path spaced from said first path backto said container zone, the improvement which comprises passing primaryelectric current through a primary transformer circuit situated adjacentthe circulating molten metal to induce secondary electric current toflow through said circulating molten metal along the entire circulatingcourse of such molten metal which acts as secondary transformer circuit,whereby to cause the heating of said circulating molten metal by theelectrical resistance heat generated during the passage of inducedelectric current therethrough.

References Cited in the file of this patent UNITED STATES PATENTS428,552 Colby May 20, 1890 1,277,523 Yensen Sept. 3, 1918 1,921,060Williams Aug. 8, 1933 2,587,793 Waldron Mar. 4, 1952 2,788,270 Nisbet etal Apr. 9, 1957 2,893,715 Harders July 7, 1959 2,893,860 Lorenz July 7,1959

